GreenBraid: Development of Resilient Flax Fibre Composites

Composites are modern, innovative materials which, depending on their design, fulfil a wide range of demanding requirements. Thus, carbon-fibre reinforced plastics can be used in sports (bicycle frames), glass fibre-reinforced plastics in concrete construction, in wind turbines or as material for chemically resistant pipes. Natural fibre-reinforced plastics offer the advantage that their production requires far less energy. However, its potential applications have still been limited up to now, as the production has not yet been sufficiently optimised. The GreenBraid project from the Institute of Textile Technology in Aachen (ITA) wants to change this.

Natural fibre-reinforced composites (NFCs) consist of a plastic matrix and a natural fibre. For this purpose, the Aachen-based researchers’ project uses flax. The biocomposites gain a stability from the incorporated natural fibres which otherwise would not be possible. Compared to glass fibre-reinforced composites (GFCs), NFCs have a low density, are medically harmless, offer a low tendency to splinter (important in vehicle manufacturing ) and are price-stable due to their independence from the price of oil. Similarly, less energy is required in their manufacture than that for GFCs or NFCs, which leads to lower manufacturing costs and reduced CO2 emissions.

To date, NFCs have mainly been used in the automotive industry. However, at a usage quantity of only 25,000 tonnes per year, they are a niche product even there. This is mainly due to the high production costs and the currently limited range of applications. To open up other areas of application, the shortness of fibre lengths is a problem, together with the associated low resilience and tensile strength. The standard manufacturing and processing methods for other composite materials cannot be readily transferred to NFCs. There is also a lack of product-oriented processes governing the characteristics.

Engine for progress:

  • Optimises product and production simultaneously
  • Offers potential energy savings of 75 per cent compared to established procedures
  • Opens up new areas of application, such as rotor blades
  • Uses native plants
  • Enhances recycling capacity
  • Fibres are not sent to landfill following end of useful life

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The picture shows a large spool of flax fibre produced at the ITA. A field hockey stick is to be produced in the project as a demonstration object. The mesh produced at the ITA was pulled over a market-standard stick for demonstration purposes.

Optimised process, regional added value

In the GreenBraid project, the characteristics of the flax fibres are to be optimised on two levels: the spinning process is adapted so as to minimise the number of rotations (twists in the yarn). This also has an influence on the next level, the braiding of the fibres. The fibres measuring just 100 mm in length are parallelised and thus a long thread such as that in glass fibre is simulated. This increases the resilience. The aim of the project is to reduce energy consumption by 75 per cent compared to previously used processes, with individual process steps being omitted and automation increased. “A broader application of NFC could also boost regional added value, since high quality bast fibres such as flax and hemp tend to be grown more commonly in Europe, while glass fibre usually has to be imported from China,” says project manager Marie-Isabel Popzyk from the ITA.

Prototype hockey stick

A hockey stick is to be produced as a prototype. The good absorption properties of the natural fibres are also brought to bear in this piece of sports equipment – properties which glass fibre does not have, and which reduce impacts on joints, arms and legs. Other areas of application such as rotor blades for wind turbines in the private sector are conceivable in the future.

The Project GreenBraid is funded by the research association Eurostars. The German partners are funded by the Federal Ministry of Education and Research.

Photo: Reimer

“GreenBraid enables bast fibres such as flax to be used in components made of fibre composites that are subject to high stresses and are utilised in vehicles or sports equipment, where previously only glass fibre could be used. The use of bast fibres enables reductions in CO2 emissions of over 30% compared to glass fibre-reinforced plastics.”

Viktor Reimer and Marie-Isabel Popzyk, GreenBraid project manager

Partners and sponsors

  • Institut für Textiltechnik (ITA) der RWTH Aachen
  • Barthels-Feldhoff GmbH & Co. KG Textilwerk
  • Holland Hockey
  • EU-Förderung